DE3735413A1 - METHOD FOR CONTROLLING THE THICKNESS OF A CARBON LAYER, IN PARTICULAR FOR THE REMOTE CONTROL OF A COAL MINING MACHINE - Google Patents

Description

The invention relates generally to coal cutting machines and in particular a method of controlling a coal cutting machine from a remote one Spot out using a medium wave communication Systems and sensors for the coal - rock interface.

Coal mining supplies have been in demand in recent years topped. This oversupply has intensified competition in mining, which in turn has led to mining operations have become more aware of the need, the cost and Reduce risks during dismantling. Contrary to the desire to cut costs to push down and increase security, the problem is that only deeper and thinner coal stocks with lower quality and higher ones Costs still left for dismantling.

In an attempt to help mining solve this dilemma, the Jet Propulsion Laboratory (JPL) has conducted a study on the evaluation of an automated long wall dismantling technique is directed (W. Zimmerman, R. Aster, J. Harris and J. High, Automation of the Longwall Mining System, JPL Publication 82-99, November 1, 1982). Amongst other things this study shows the need to use remote control technology for long wall To develop Schräm works.

Remote control for the cutting machine requires that the Coal-rock interface at a short distance to get the miners out of the to keep out dangerous coal mining front. The continuous and Longwall mining requires that the miner get close to the coal cutting edges (Roller) so that he can see the mining horizon and the Can prevent cutting edges from hitting rock. With this The miner at the cutting machine is constantly in a dangerous process Area. If the cutting edges of the cutting machine are on rock sparking sparks can ignite methane and coal dust cause. When sandstone is cut into the roof or floor, it becomes silica sand  produced in the dust, so that the permissible limit values for the Dust content in the breathing air may be exceeded. In the mining operation this danger is often reduced by the fact that the rate of delivery of the cutting machine is reduced that only in the direction of the dismantling front ventilation Airflow is milled, or the irrigation is intensified to the dust cloud to disperse. Wear also leads to the dust problem the milling drum and the bearings of the mechanical drive components often to increased downtime and maintenance problems.

Another requirement for the effective automation of a long wall dismantling system is the development of a reliable remote control communication system. Various long wall manufacturers in the USA and Europe currently offer VHF (very high frequency) and LF (low frequency) remote control systems at. The LF system consists of a control connection from the Obertor command center to the cutting machine via the AC power cable. The LF system is limited as it is remote control from somewhere along the line Dismantling front not possible. VHF and UHF systems work satisfactorily with signal propagation paths running in the field of view, um to control continuous mining equipment and roof bolts. The However, technology fails when it comes to remote control of trains in tunnels and loading areas, as they are used in block construction. The reasons why VHF and UHF systems do not work in these situations, they are too seek that VHF and UHF signals suffer from very strong attenuation when they propagate down the waveguide that passes through the shield and Pan section is generated, reliable control is on line of sight operation limited, waves along the mining front can control the area limit, and the reflected signal energy from the steel long wall supports provides zeros in the transmission waves. Because of the VHF and Problems related to UHF transmission is the radio transmission signal in the "dead control" zero zone below that for a low bit error rate is required. This too low bit rate results in command signals are incorrectly decoded or not responded to at all becomes.  

To control the cutting machine (or a continuous mining machine) To enable from a safe distance are different Attempts have been made to develop a coal-rock sensor technology. In Europe and the United States, researchers have sensor technology based on natural Radiation background examined. The use of natural Background radiation from the layers above it allows one such a system to measure the coal thickness above the cutting machine and keep up when working with the cutter; in some geological Formations, however, this sensor does not work reliably. Others, similar ones Applications of techniques include the use of acoustic Apparitions and the "sensitive pimple" for measuring the seam thickness and to detect the coal-rock interface, and the study of Microwave measurement techniques by researchers at the National Bureau of Standards. The main thrust of the sensor for natural background radiation, at Acoustic and microwave measurement techniques lay in the control possibilities of the Bergmanns on the cutting machine so that it increases the could mine the maximum possible amount of coal.

Other sensors have been developed to solve mining front alignment problems, which contributed to many conveyor and ladle line failures. One of these Sensors was the yaw measurement sensor developed by the Benton Corporation has been. This sensor measures angular deviations in the pan section and transfers information to a computer. The computer determines that Position of the cutting machine and the straightness of the front conveyor. A U.S. government report reports on NASA's Marshall investigation Space Flight Center Longwall Program reports the operating behavior several cutting machine and conveyor sensors, and then design problems checked that when retrofitting the most promising sensors occur in the cutting machine and conveyor.

Finally, Chang and Wait revealed one in a basic essay theoretical proposal to determine a resonance loop antenna as a probe the roof thickness in a coal mining operation (D. Chang and J. Wait, An Analysis of a Resonant Loop as an Electromagnetic Sensor of Coal Seam Thickness, Proceedings of URSI Conference on Remote Sensing, LaBaule, France (April 28 - May 6, 1977).

The object of the invention is therefore to provide an improved method for Remote control of a long wall cutting machine or continuous mining machine to make available with which it is possible to extract the miners to keep out of the dangerous coal milling zone.

The invention is also intended to provide an improved method for remote control a long wall cutting machine or continuous mining machine made available using a reliable communication system will.

The invention is also intended to provide a reliable remote communication system that can easily be made available on a long wall cutting machine or continuous mining machine can be coupled.

The invention is also intended to provide an improved method for remote control a long wall cutting machine or continuous mining machine be made available using a coal-rock interface sensor becomes.

In short, one embodiment of the invention has a medium wave (MF = medium frequency) remote control system that is magnetic with the AC power cable the cutting machine is coupled at a remote location. Inside the cutter is a medium wave receiver on the AC cable coupled using a ferrite (C-core) line coupler. The cutting machine is equipped with a coal-rock interface sensor, which allows remote control of the mining process.

An advantage of the invention is that the remote control process of the long wall Mining machine or continuous mining machine the dangerous coal milling zone.

Another advantage of the invention is that the coal-rock interface Sensor reduces the likelihood that a cutting edge of the Cutting machine meets rock.  

Another advantage of the invention is that a thin layer of carbon can remain on the roof.

Yet another advantage of the invention is that the remote Communication system reliably transfers data.

Another advantage of the invention is that the remote Communication system easily connected to the long wall cutting machine or continuous mining machine can be coupled.

These and other objects and features of the invention emerge in detail from the following description in conjunction with the drawing; in this shows

Figure 1 is a diagram of a remote controlled coal cutting machine according to the invention.

FIG. 2 shows an expanded partial block diagram of the electronic components within the explosion-proof housing according to FIG. 1;

Fig. 3 is a body-worn shoulder strap remote control transmitter; and

Fig. 4 graphically data on the conductivity as a function of the carbon layer thickness, as they are obtained with a coal-rock-Interfacial sensor of FIG. 1.

In Fig. 1, a remote controlled coal milling machine is shown, which is generally designated by the reference numeral 10 and which is suitable for carrying out the remote controlled mining method according to the invention. The coal milling machine 10 can be either a long wall cutting machine or a continuous mining machine. A cutting machine 12 includes an upper gate arm 14 and a lower gate arm 16 . The upper gate cantilever arm 14 includes an upper gate carbon milling drum 18 and the lower gate cantilever arm 16 contains a lower gate carbon milling drum 20 . A coal-rock interface sensor 22 is mounted on the top of the cutter 12 behind the top gate boom 14 . The sensor 22 is embedded in a plate 24 which is mounted on a steel tube 26 , with a top cover 28 remaining free. A cable 30 that runs through a sensor arm 31 connects the sensor 22 to a sensor control unit 32 . A wheel 34 attached to the steel tube 26 with an arm 36 provides an air gap 38 with a width "w" by pressing on a layer of carbon 40 . The carbon layer 40 has a thickness "t" and lies under a rock layer 42 . An explosion-proof housing 44 is located within the cutting machine 12 and contains the sensor control unit 32 , a remote control unit 46 for the upper gate and a remote control unit 48 for the lower gate. A control unit 49 for an electrohydraulic system is attached to the upper gate control unit 46 , as well as an upper gate RF signal coupler 50 which actuates an electrohydraulic solenoid valve and hose 51 . A sub-port RF signal coupler 52 and a sub-port electrohydraulic solenoid valve and hose 54 are attached to the sub-port control unit 48 . An AC cable 56 is connected to a power supply 58 . A loop antenna 60 is magnetically coupled to the cable 56 with a magnetic field 61 . The loop antenna 60 is connected with a wire 64 to a transmitter 62 . An interface 66 is connected to the transmitter 62 by a wire 68 .

Fig. 2 shows an expanded partial block diagram of the electronic components contained in the housing 44. The top gate remote control unit 46 includes a control panel 70 which is connected to a receiver 72 which is connected to a decoder 74 . The decoder 74 is connected to a contactor control unit 76 which is connected to a plurality of switches 78 , all of which are included in the electro-hydraulic control unit 49 . A second set of components similar to that shown in FIG. 2 is required for the under-gate remote control unit 48 .

FIG. 3 shows a remote control transmitter belt to be worn on the body, generally designated 80 . The belt 80 is designed to be worn by a miner 82 . As shown in FIG. 3, the interface 66 , the transmitter 62 and the loop antenna 60 according to FIG. 1 are all provided on the belt 80 . Interface 66 includes a plurality of push button control switches 84 . A battery 86 provides power to the transmitter 62 and a bracket 88 is provided to adjust the belt 80 .

FIG. 4 graphically shows a representative relationship between conductivity and carbon layer thickness ( "t" in FIG. 1). This is the type of data that is collected with the coal-rock interface sensor 22 shown in FIG. 1. The data in Fig. 4 show that there is a conductivity value G _a around which the conductivity G oscillates and to which G converges at infinite thickness. The discrete thickness at which G is equal to a value G _a becomes the control thickness "t _D ". If the measured conductivity becomes greater than G _a , this indicates that a correction of the position of the milling drum 18 is necessary. If the measured conductivity G becomes smaller than G _a , this indicates that a correction in the opposite direction is necessary.

In the preferred embodiment of the invention, interface 66 of FIG. 1 is a keyboard that is mounted on the face of transmitter 62 , as illustrated in FIG. 3. The push button control switches 84 emulate the switches 78 on the cutting machine so that commands sent by the transmitter 62 in the electro-hydraulic control unit 49 of the cutting machine produce the same responses as the switches 78 . With the transmitter 80 to be worn on the body and the control units 46 and 48 in the flame-proof housing 44 of the cutting machine, the system enables independent remote control of the following cutting machine functions:

The transmitter 62 and the receiver 72 operate in the medium wave range between 300 and 1000 kHz. The frequency plan for independent operation of each of the two rollers 18 and 20 requires two transmitter carrier frequencies (f ₁, f ₁ *) . These frequencies should be at least 50 kHz apart. 400 and 520 kHz are proposed as frequencies. The RF line couplers (current transformers) 50 and 52 are used to couple command and control signals from the AC cable 56 . This type of coupling is unique in that it is a ferrite coupler that is small in size so that it can be constructed into the explosion-proof housing 44 . Mounting the coupler in an explosion-proof housing improves the reliability of the equipment. In contrast, exposed antennas that can be easily damaged are required with VHF and UHF equipment. The receiver output signal contains control information for the electro-hydraulic system of the cutting machine. The digital control signal is applied to decoder 74 , which in turn processes the digital signal such that algorithms are called that minimize the bit error rate. The control signals (called "command signals") are encoded (in the remote control transmitter 62 ) with a highly structured digital code word. The code word contains the address and command data. To minimize errors, decoder 74 only accepts digital control signals with the correct address; Furthermore, the control signals must be correctly received two or three times, with at least two of the received words having to be identical before the code is validated. A microphone in the receiver decoder detects every error in the digital command data. This ensures that only correct commands are given to the cutting machine's electro-hydraulic system. The decoded output signal is then sent to the contactor holder 76 , which forms an interface (relay contacts) to the existing cutting machine control 78 (push buttons and switches).

The digital control signal structure for each word sent by transmitter 62 includes a 15-bit preamble which is used to synchronize remote control decoder 74 so that the address and command data can be retrieved; furthermore, only three address bits (TXID) are required for the cutting machine and twelve functions are required in most remote control applications .

The technical reason for sending a sequence of identical words is that the bit error rate of the digital word can be improved. The bit error rate of n repeated words is given by

P _T = ( P _A ) ⁿ

where P _{A is} the probability of a bit error in a single word. For example, if the bit error rate is 10 ^-3 , sending two identical words would improve the bit error rate to 10 ^-6 .

Each word is encoded using a Manchester format. The Manchester command data is given in transmitter 62 to a frequency shift keying encoder. A frequency shift keying decoder 74 is used in the remote control unit 46 to recover the command data.

The frequency-modulated carrier is used in the data transmission system. The carrier frequency is in the medium wave range and is by frequency shift keying modulated (1200 Hz and 2200 Hz).

A phase change in the Manchester code indicates the logical bit status. A Manchester code downward transition (phase) occurs in the middle of the data bit without returning to zero. A Manchester code upward transition shows one logical "zero". The transition in the Manchester code carries the clock synchronization signal (half clock rate).

The first three logic bits identify the address (sender ID = identification) and add a security measure to the code structure. The following twelve control logic bits are used for independent (simultaneous) control functions.

The microprocessor's read only memory contains the Manchester decoding algorithms, which decode the Manchester code checks for cutting machine operator errors and excites the corresponding output line (s).  

If any push button or switch on the transmitter is pressed, the bit status in the control bit sequence changes to logic "1". The microprocessor algorithm decodes the bit as logic "1" and excites the corresponding microprocessor output port. No parity is transmitted with the code; However, error checking is carried out by the following tests:
No data in C 16 (end of work overlap code collision).
No data before the start bit.
Transmitter identity must be correct as set by switches on the microprocessor and transmitter circuit boards.
Simultaneously pressing the pushbuttons for the boom arm, cover, piece crusher or conveying speed are ignored.
Pressing the conveyor speed buttons causes the conveyor speed servo to be programmed to zero.

Each control word transmission period is

Pressing a button or a switch ensures that several immediately Words are sent, two of which are decoded as identical have to. The transmitter also sends a monitoring signal every 10 seconds. A failure of the detection or monitoring is intended to excite the delivery stop command function. The microprocessor algorithm can be modified to achieve many additional tax strategies.

The use of the coal-rock boundary layer sensor 22 of FIG. 1 is important to the invention because, with current cutting machine equipment, the miner cannot determine where the coal-rock boundary layer is until it is encountered. The miner can try to be careful by trying to leave a significant layer of coal on the roof, or he can try to stop milling as soon as possible when rock is encountered. In the first case, the miner can leave more coal on the roof than necessary, which may reduce the overall yield by 5 to 6%. In the second case, the roof control problems increase if there is not enough coal left on the roof. In marginal seams, the coal closest to the roof can contain a higher percentage of sulfur and ash, so if it is removed, the quality of the coal mined will be reduced.

If the miner cuts into the rock, additional problems arise. When the cutting edges of roller 18 hit rock, flying sparks can cause methane and coal dust ignitions. Silicate sand in the dust makes it difficult to comply with the dust protection regulations. Furthermore, the coal is contaminated, so that the overall coal quality is deteriorated. In addition to these problems, milling in rock increases the wear of the milling drum 18 and the mechanical component of the cutting machine 12 and leads to additional maintenance and downtimes. Any possible option to reduce these problems increases the cost.

By using a reliable coal-rock boundary layer sensor 22 , a thin layer of coal "t" can remain on the roof, reducing roof control problems, safety, and costs while improving production and coal quality. For example, under shale and clay stone roof rock 42 prevents the thin carbon film that, by admission of air to the rock 42 of this chipping. This helps to ensure a competent roof in the front area.

Security can be further improved if the sensor 22 is used in connection with a remote control connection. Currently, the miner must be very close to the carbon cutting edges of roller 18 so that he can see the milling horizon and prevent the cutting edges from hitting rock. With a remote control connection, the miner receives information about the coal layer thickness "t" at a remote location. This enables the miner to control the cutting machine 12 far from the dangerous milling zone. If the miner controlling the cutter 12 is out of the dust cloud and away from the dangerous mining front, productivity continues to increase because milling can be done in either direction from the ventilation airflow at the mining front.

The electronic construction of the carbon-rock interface sensor 22 used in the present invention is based on measuring the input admittance of a tuned loop antenna. The theoretical work most applicable to sensor 22 was done by Chang and Wait and, as mentioned at the beginning, was published.

With proper shielding, the electrical properties of a Resonance loop only influenced by the roof structure. From one control there are no significant disruptions due to nearby mining facilities.

The sensor antenna is mounted in the vertical steel tube 26 , which is located approximately in the middle of the conveyor 12 , and directly below the carbon cover 40 . The electronic unit 32 , which contains the necessary circuitry, is mounted in the explosion-proof housing 44 on the conveyor 12 . Housing 44 provides a dust-free environment for the circuit board assembly.

The input admittance of the resonant loop antenna is measured in real time. The admittance is given mathematically by:

Y = G + jB

in which

G = input conductance of the loop antenna in Siemens and B = input reactive conductance

There are several ways to measure antenna input admittance. The two methods commonly used in commercial instrument designs used are:

Directional Coupler and
Directional bridge.

Because multiple operating frequencies are not with a resonant loop antenna directional coupler design is used. The determination of the admittance is based on the measurement of the load level reflection coefficients, represented mathematically by

in which
Z _L = load level impedance and Z _O = characteristic impedance of the transmission line that connects the measuring unit to the load level.

The oscillator circuit generates an RF test signal that is sent to the directional coupler is created, which is completed with the antenna load level admittance is. The vectorial tension ratio components of the reflected to the incident wave are detected. The reflection coefficient is defined as:

wherein
V _ref = voltage level of the reflected wave and V _inc = voltage level of the incident wave.

The reflection coefficient and the impedance value result from:

The input admittance is the reciprocal of Z _L :

Y = 1 / Z _L = G + jB

For a voltage signal of amplitude one, the value of G corresponds exactly to the radiated power from the antenna. A microprocessor uses the phase and amplitude measurement data to determine the reflection coefficient and the value of G.

To use the coal-rock interface sensor, the sensor must be calibrated by taking measurements at various incremental values of coal thickness "t" . In order to carry out this calibration, the cutting machine mills vertically through the coal layer 40 to the rock 42 , switches back an incremental step from the rock 42 , penetrates transversely into the coal layer 40 for a short distance and switches back an incremental vertical distance from the rock 42 . This procedure is repeated with measurements being made and stored for each of these thicknesses " t ". This calibration provides a discrete set of allowable thicknesses "t" for which control is possible.

Next, the miner selects the desired thickness "t" of coal to remain on the roof / floor from the set of allowed values. The cutting machine must then be brought to a position corresponding to this thickness; this is done by milling in rock 42 and switching back by the appropriate distance.

The cutting operation then begins. While the cutting machine 12 is running forward, the sensor 22 monitors its position in relation to the rock 42 by comparing ongoing measurements with the stored calibration data. When the measured value becomes larger than the stored value for the specific thickness "t" , a light is turned on, indicating that correction in a certain direction (upwards or downwards) is necessary. If the measured value is less than the stored value, a light is switched on, which indicates that a correction in the opposite direction is necessary. The necessary corrections can either be made at the location of the cutting machine, or from a remote location using transmitter 62 .

In the preferred embodiment of the invention, the coal-rock interface sensor 22 is a tuned loop antenna with no moving parts. The loop and cable connection 30 , which leads the UHF signal to the antenna, is embedded in a solid, wear-resistant, high-strength plastic plate 24 . The plate is mounted in a strong steel tube, with only the top of the plate 28 being exposed.

Claims (6)

1. A method of controlling the thickness of a layer of coal remaining in a coal seam adjacent to a layer of rock consisting of:

• a) calculating a control guide value;
• b) bringing a sensor for conductivity measurement into a position near the coal seam in such a way that the control conductance is registered by the sensor;
• c) moving the sensor transversely along the coal seam at a constant distance immediately behind a coal milling drum positioned to mill into the coal seam with a discrete cutting depth; and
• d) Resetting the cutting depth of the carbon milling drum when the sensor dictates a specified change in the conductance compared to the control conductance.

2. The method of claim 1, wherein the step of calculating the control guide value consists of:

• a) using the coal milling drum to mill through the coal seam until the rock layer is encountered;
• b) adjusting the milling depth of the coal milling drum by an incremental amount such that a first coal layer remains between the rock layer and the coal milling drum after the coal milling drum is advanced into the coal seam;
• c) advancing the coal milling drum across the coal seam by an incremental distance;
• d) stopping the feed;
• e) using the sensor to measure a first conductivity value in the first carbon layer;
• f) storing the first conductivity value in a microprocessor;
• g) repeating steps (b) through (f) such that a plurality of conductivity values are obtained for a plurality of coal layers, each subsequent coal layer having a greater thickness than the preceding coal layer; and
• h) using the microprocessor to calculate the control conductivity value of at least some of the many conductivity values.

3. The method according to claim 1, wherein the step of readjusting the cutting depth of the carbon milling drum, after the sensor faces a specified change in conductivity the control conductivity value is detected at a remote location using a remote control medium wave transmitter becomes. 4. Method for remote control of the mechanical functions of the electro-hydraulic system of a coal mining machine, consisting of

• a) a mobile medium wave transmitter is inductively coupled to an AC cable leading to the coal mining machine;
• b) the AC cable is coupled to a remote control unit within the coal mining machine using a ferrite line coupler;
• c) command and control signals are sent from the mobile medium wave transmitter to the remote control unit; and
• d) Command and control signals are sent from the remote control unit to an electro-hydraulic system control unit.

5. The method of claim 4, wherein the coal mining machine is a long wall Is cutting machine. 6. The method of claim 4, wherein the coal mining machine is a continuous Mining machine is.